Vehicle systems may include various vacuum consumption devices that are actuated using vacuum. These may include, for example, a brake booster. Vacuum used by these devices may be provided by a dedicated vacuum pump. In still other embodiments, one or more ejectors may be coupled in the engine system that may harness engine airflow and use it to generate vacuum.
As such, an amount of vacuum generated at an ejector can be controlled by controlling the motive air flow rate through the ejector. In one example, this may be achieved through the use of a large, electric solenoid valve positioned upstream of the ejector. By controlling the opening of the solenoid valve, the amount of rate and air flowing through the ejector can be varied, thereby adjusting vacuum generation as engine operating conditions change. However, the inventors herein have recognized that such solenoid valves can add significant component and operating costs to the engine system. As a result, the cost of including the valve may reduce the advantages of ejector vacuum control. As such, if the air flow through the ejector is not controlled, the full vacuum generation potential of the ejector may not be taken advantage of. Further, loss of boost pressure may result from reverse flow through the ejector, as may occur during conditions of high boost pressure.
Thus in one example, the above issue may be at least partially addressed by a method of operating an engine that enables lower cost ejector vacuum control. The method includes adjusting a valve coupled upstream of an intake ejector based on boost pressure, the valve adjusted to control motive flow into the ejector from upstream of a compressor.
Further, in some examples, the method may include opening the valve responsive to vacuum level at a vacuum reservoir to vary a motive flow through an ejector coupled across an intake throttle, the valve coupled upstream (or downstream) of the ejector. The vacuum may be drawn at the ejector and the drawn vacuum may be stored in the vacuum reservoir. In this way, motive flow can be increased in response to a need for vacuum replenishment without sacrificing boost pressure.
For example, an engine system may include an ejector coupled across an intake throttle in a bypass passage. A vacuum-actuated valve may be coupled upstream of the ejector to vary a motive flow through the ejector. The vacuum-actuated valve may be directly coupled to the vacuum reservoir with no solenoid in between, and the valve may be coupled to an outlet of a compressor. In such an embodiment, the opening or closing of the vacuum-actuated valve may be directly adjusted based on the vacuum level of the reservoir and further based on boost pressure. When the vacuum level in the reservoir is lower (e.g., below a threshold) and boost pressure is lower (e.g., below a threshold pressure), the valve may be actuated open so as to increase motive flow through the ejector. This increased motive flow results in a corresponding increase in vacuum generation at the ejector, which can then be used to replenish the vacuum reservoir. In contrast, when the vacuum level in the reservoir is higher (e.g., above the threshold) and/or the boost pressure is higher (e.g., above the threshold pressure), the valve may be actuated closed so as to decrease motive flow through the ejector and prevent flow of air from the intake manifold to the inlet of the compressor. This decreased motive flow results in a corresponding decrease in vacuum generation at the ejector. By only allowing motive flow when the vacuum reservoir needs it's vacuum replenished, that motive flow has the least opportunity to cause air flow disturbances where engine air flow rate is in excess of desired engine air flow rate. Further, by only allowing motive flow when boost pressure is low, loss of boost may be reduced.
It will be appreciated that in alternate embodiments, the ejector may be located such that the high pressure side of the ejector is downstream of the air filter, the crankcase, and at the compressor outlet. Likewise, alternate taps for the low pressure side of the ejector may be downstream of the air filter and the crankcase.
In this way, motive flow through an ejector can be adjusted based on vacuum requirements and further based on boost pressure. By opening a vacuum-actuated valve, coupled in series with the ejector, in response to a drop in vacuum levels at a vacuum reservoir, motive flow at the ejector can be increased to replenish the reservoir. Then, once the vacuum is sufficiently full, the valve may be closed. Overall, the vacuum generation efficiency of the ejector and ejector motive flow control is improved without substantially increasing component cost or complexity. Additionally, boost pressure may be maintained by closing the valve when boost pressure exceeds a threshold.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.